Process for treating a hydrocarbon or hydrocarbon mixture which is contaminated by small amounts of organic fluorine compounds



Patented Oct. 7, 1947 PROCESS FOR TREATING A HYDROCARBON R HYDROCARBON MIXTURE WHICH IS CONTAMINATED BY SMALLAMOUNTS OF ORGANIC FLUORINE COIWPOUNDS Carl B. Linn, Riverside, 111., assignor to Universal Oil Products Company, Chicago, 111., a corporation of Delaware No Drawing. Application October 27, 1945, Serial No. 625,099

This invention relates to a process for treating a hydrocarbon or hydrocarbon mixture which is contaminated by small amounts of organic fluorine compounds to remove fluorine therefrom. More specifically, it relates to the treatment of hydrocarbons produced synthetically in the presence of an active fluoride catalyst to remove small amounts of organically combined fluorine present in compounds admixed with the hydrocarbon or hydrocarbon mixture.

The invention is particularly adapted to the treatment of hydrocarbons produced by the allwlation of isoparafllnic hydrocarbons with oleflnic hydrocarbons or with alkyl fluorides using active fluoride catalysts including hydrogen fluoride or fluoride mixtures comprising essentially hydrogen fluoride and boron fluoride. The process is also applicable to the removal of alkyl fluorides from propane and butane fractions, said fractions being recovered from the gaseous products discharged from an alkylation plant in which isobutane is alkylated by oleflns present in a propane-propylene or butane-butylene fraction.

An object of this invention is to defluorinate a hydrocarbon or hydrocarbon mixture contaminated by relatively small amount of organic fluorine compounds, particularly alkyl fluorides.

Another object of this invention is to dehydrofluorinate an isoparaifln alkylation product formed in the presence of an active fluoride catalyst.

A further object of this invention is to remove alkyl fluorides from hydrocarbon conversion products formed in the presence of an active fluoride catalyst. 3

A still further object of this invention is to remove alkyl fluorides from a fraction of normally gaseous parafllnic'hydrocarbons recovered from the products formed in the alkylation of isobutane by oleflns present in a Ca-C4 hydrocarbon fraction.

Another object of this invention is to remove ethyl fluoride from a propane fraction recovered from the products formed in the alkylation of isobutane in the presence of hydrogen fluoride with a propane-propylene fraction containing a relatively small amount of ethylene.

One specific embodiment of the present invention comprises a process for treating hydrocarbon material containin as an impurity a relatively small percentage of organically combined fluorine to remove fluorine therefrom which comprises contacting said material with chlorosulionic acid at dehydrofluorinating conditions of 14 Claims. (01. 260676) temperature and pressure, and recovering the treated hydrocarbon material.

Another embodiment'oi! the present invention comprises a process for treating hydrocarbons recovered from an alkylation process in which an isoparaffln is alkylated with an olefin in the presence of an active fluoride catalyst, by treating said hydrocarbons with chlorosulfonic acid at dehydrofluorinating conditions of temperature, pressure and time, and recovering the treated hydrocarbons.

The alkylation of branched chain paramnic 11y.- drocarbons such as 'isobutane and isopentane with oleflnic hydrocarbons, particularly the oleflnic hydrocarbons present in cracked gases, produces saturated liquid hydrocarbons utilizable as constituents of gasoline of high antiknock value. By this means relatively low boiling isoparamnic hydrocarbons are aikylated with low boiling oleflns and thereby converted into materials of higher boiling point and high antiknock values. The higher boiling hydrocarbons so formed from low boiling isoparaflins and olefins in the presence of an active fluoride catalyst including hydrogen fluoride or mixture of hydrogen fluoride and boron fluoride, frequently contain small amounts of organic fluorine compounds which are not readily removable by washing with caustic and water or by fractional distillation.

These contaminating fluorine compounds which are thu present in aikylation hydrocarbon mixtures are frequently due to the interaction of hydrogen fluoride with oleflns to form alkyl fluorides. Some alkyl fluorides are more stable than others in the presence of active fluoride catalysts. Thus, ethyl fluoride is more stable than some ofthe higher molecular weight alkyl fluorides in an alkylation reaction mixture and is not converted completely into parafllnic alkylation products but admixes with the hydrocarbon products. Some higher boiling alkyl fluorides and other organic fluorine compounds may also remain in hydrocarbon alkylation products. Because of its high stability, boiling point, and the fact that it forms with propane an azeotrope boiling at --47 C., ethyl fluoride is found in the propane fraction recovered from an allwlation ene and higher olefins, but in these cases the alkylation product also contains small quantities and an olefin of higher molecular weight than ethylene.

Although the fluorine content of the hydrocarbon product of gasoline boiling range resulting from an alkylation treatment is rarely very high,

the presence of fluorine is undesirable both from the standpoint that the combustion products of such a fuel are corrosive, as well as the fact that the antiknock value of the gasoline, generally expressed by the term octane number is reduced considerably either when the gasoline is used as such, or when a small amount of an antidetonating agent such as lead tetraethyl is added thereto. Thus it may be shown that gasoline fractions containing 0.1% by weight of fluorine have inferior antiknock properties, particularly as concerns their response to lead tetraethyl, as compared to the otherwise same material which contains substantially no fluorine compounds. present invention offers a method for reducing the fluorine content of the hydrocarbon alkylatlon product to an amount where this adverse eifect is negligible.

Also, propane and normal butane which are not alkylated during the alkylation treatment of an isoparafiln with olefins present in a C3 or a C4 hydrocarbon fraction are recovered from alkyiation products and marketed as bottled gas for use as domestic fuels and for various industrial uses. Such recovered propane and normal butane fractions are sometimes contaminated by ethyl fluoride and other organic fluorine compounds formed incidentally in the alkylation treatment and it is desirable that these propane and butane fractions be freed from fluorine compoundsbefore being soutilized as fuel.

It is much more difficult to dehydrofluorinate ethyl fluoride than the other alkyl fluorides which may be encountered in products of the hydrogen fluoride alkylation process. It has been observed that alkylation plants'which charge a propanepropylene feed stock to the alkylation reactor produce ethyl fluoride from the ethylene which sometimes contaminates the C: feed stock. This ethyl fluoride tends to go through the plant unchanged and finally appears in the propane fraction recovered from th effluent gases. The methods used heretofore for removing organic fluorine compounds from-alkylate such as passage through heated contactors containing bauxite or aluminum do not cause the dehydrofluori-' nation of ethyl fluoride and consequently are ineffective for producing a propane fraction substantially free from fluorine. My process, however, does defluorinate not only the gasoline bolling range material but also propan and butane and makes it possible to produce substantially fluorine-free propane and butane fractions.

As indicated above, ethyl fluoride is more stable than the higher alkyl fluorides encountered in the products of the hydrogen fluoride alkylation process. Possibly one reason for this difference in stability of the alkyl fluorides is the fact that ethyl fluoride is a primary alkyl fluoride, while the alkyl fluorides produced from propylene and higher oleflns are either secondary or tertiary alkyl fluorides. I have found that when propane which is contaminated by small amounts of ethyl fluoride is treated at about 25C. .with chlorosulfonic acid, the fluorine content is reduced more than 98% to give a propane fraction containing The 4' only about 0.01%, or less, by weight of fluorine from a contaminated material containing 1.0% fluorine present as ethyl fluoride.

One method of preparing chlorosuifonic acid consists in passing anhydrous hydrogen chloride into fuming sulfuric acid (80% 50:) until hydrogen chloride is no longer absorbed. The resultant product upon being subjected to fractional distillation loses some hydrogen chloride and then chlorosuifonic acid distills over at a temperature between 150 and 165 C. Chlorosulfonic acid is also obtained by the direct union of hydrogen chloride and sulfur trioxide, by the action of chlorine or sulfur chloride upon concentrated sulfuric acid, by the action of sulfuric acid on thionyl chloride, by'the action of a little water or concentrated sulfuric'acid on sulfuryl chloride, and by the action of imperfectly dried chlorine on moist sulfur dioxide in the presence of platinum black at a red heat.

According to the process of the present inven tion, hydrocarbon material contaminated by organic fluorine compounds is freed from a substantial proportion of such organically combined fluorine by treatment with chlorosuifonic acid at a temperature of from about -50 to about 150 C. and preferably at a temperature of from about 0 to about 50 C. The process is carried out at atmospheric pressure or at a superatmospheric pressure sufllcient to maintain the fluorine-containing hydrocarbon or hydrocarbon mixture in substantially liquid phase.

The treatment of the hydrocarbon or hydrocarbon mixture with chlorosuifonic acid is effected in either batch or continuous types of treatment. In batch type operation, one volume of the hydrocarbon or hydrocarbon mixture contaminated by organic fluorine compounds is agitated with from about 0.1 to about 2 volumes of chlorosuifonic acid at a temperature of from about 50 to about 150 C. and at a pressure sufficient to maintain liquid phase operation and for a time generally of from about 0.1 to about 3 hours. The resultant reaction mixture is then separated into a chlorosuifonic acid layer and a hydrocarbon layer and the latter is washed, dried, and distilled or otherwise treated to recover the desired hydrocarbon or hydrocarbons substantially free from fluorine-containing compounds, while the used chlorosuifonic acid is returned to the reactor for further use in treating an additional quantity of the hydrocarbon charging stock.

Continuous treatment of a hydrocarbon containing organically combined fluorine is effected by passing said hydrocarbon and a proportioned amount of chlorosulfonic acid through a baiiled fonic acid is then withdrawn from the separator and a portion of it is recycled to further use in treating an additional quantity of the mentioned charging stock.

The action between an alkyl fluoride and chlorosulionic acid appears to proceed according'to between ethyl fluoride and chlorosulfonic acid:

These equations indicate that chlorosulfonic acid reactswith the alkyl fluoride in stoichiometric proportions, forming an ester of fluorosulfonic acid and accordingly functions not as a catalyst, but as a reagent for defluorinating the hydrocarbon material containing the alkyl fluoride. However, chlorosulfonic acid is an attractive defluorinating agent because of its low cost, its efliciency in removing fluorine, and its physical properties which are well adapted to the general process employed for carrying out such operations.

The defluorination treatment referred to herein may also be carried out by producing chlorosulionic acid in situ by commingling sulfur trioxide and hydrogen chloride with the fluorine-containing hydrocarbon mixture, these materials being commingled at the point where the defluorination is to be eflected.

The following examples are given to show results obtained in the operation of the process, but they are not to be considered to unduly limit the broad scope of the invention.

Example I 100cc. (173 grams) of chlorosulfonic acid was sealed in a, rotatable steel autoclave or 850 cc. capacity and then 50 grams of a propane fraction containing ethyl fluoride as an impurity (analyzing 1% fluorine) was introduced to the autoclave which was then rotated at 25 C. for 3 hours. The autoclave and its contents then stood at 25 C. for 15 hours after which the propane was released through caustic soda solution and collected. The

propane so recovered contained 0.012% fluorine,

thus showing that more than 98% by weight of the fluorine had been removed.

Example II In another run, ethyl fluoride was absorbed completely when passed slowly into chlorosulfonic acid at 25 C. In this run, hydrogen chloride was evolved in an amount approximately equivalent to the molecular quantity of ethyl fluoride absorbed by the chlorosulfonic acid. Thusit appeared that a fluorine-chlorine exchange reaction occurred between the ethyl fluoride and chlorosulfonic acid. Although the mechanism of the defluorination reaction is not known completely, it may be explained by the equations given above which indicate that ethyl fluoride and chlorosulfonic acid react to form ethyl chloride and fluorosulfonic acid. The resultant ethyl chloride and fluorosulfonic acid may then interact to form remove fluorine therefrom which comprises contacting said hydrocarbon material with chlorosulfonic acid at defluorinating conditions of temperature and pressure, and recovering the treated hydrocarbon material.

2. A process for treating a hydrocarbon material containing as an impurity a relatively small percentage of an alkyl fluoride to remove fluorine therefrom which comprises contacting said hydrocarbon material with chlorosulfonic acid at defluorinating conditions 01' temperature and pressure, and recovering the .treated hydrocarbon material.

3. A process for treating a hydrocarbon material containing as an impurity a relatively small percentage of organically combined fluorine and produced by catalytic alkylation of an isoparafflnic hydrocarbon with an oleflnic hydrocarbon in the presence or an active fluoride catalyst which comprises treating said hydrocarbon material with chlorosulfonic acid at defluorlnating conditions or temperature and pressure, and recovering the treated hydrocarbon material.

4. A process for treating a hydrocarbon material containing as an impurity a. relatively small percentage of organically combined fluorine and produced by catalytic alkylation of an isoparaffinic hydrocarbon with an oleflnic hydrocarbon of higher molecular weight than ethylene in the presence of a hydrogen fluoride catalyst which comprises treating said hydrocarbon material with chlorosulfonic acid at defluorinating conditions of temperature and pressure, and recovering the treated hydrocarbon material.

5. A process for treating a hydrocarbon material containing as an impurity a relatively small percentage of organically combined fluorine to remove fluorine therefrom which comprises contacting said hydrocarbon material with chlorosulfonic acid at a temperature of from about -50 to about- C., and recovering the treated hydrocarbon material.

6. A process for treating a hydrocarbon material containing as an impurity a relatively small percentage of organically combined fluorine to remove fluorine therefrom which comprises contacting said hydrocarbon material with chlorosulfonic acid at a temperature of from about 50 to about 150 C. and at a pressure willcient to maintain the hydrocarbon material in substantially liquid phase, and recovering the treated hydrocarbon material.

'7. A process for treating a hydrocarbon material containing as an impurity a relatively small percentage of an alkyl fluoride to remove fluorine therefrom which comprises contacting said hydrocarbon material with chlorosulfonic acid at a temperature of from about 50 to about 150 C., and recovering the treated hydrocarbon material.

8. A process for treating a hydrocarbon material containing as an impurity a relatively small percentage of an alkyl fluoride to remove fluorine therefrom which comprises contacting said hydrocarbon material with chlorosulfonic acid at a temperature of from about 50 to about 150 C. and at a pressure suflicient to maintain the hydrocarbon material in substantially liquid phase, and recovering the treated hydrocarbon material.

9. A process for treating propane containing as an impurity a relatively small percentage of organically combined fluorine to remove fluorine therefrom which comprises contacting said propane with chlorosulfonic acid at defluorinating conditions of temperature and pressure, and recovering the treated propane.

10. A process for treating butane containing as an impurity a relatively small percentage of 7 organically combined fluorine to remove fluorine therefrom which comprises contacting said butane with chlorosulfonic acid at defluorinating conditions of temperature and pressure, and recovering the treated butane.

11. A process for treating a normally liquid paraflinic hydrocarbon mixture containing as an impurity a relatively small percentage of organically combined fluorine to remove fluorine therefrom which comprises contacting said normally liquid paramnic hydrocarbon mixture with chlorosulfonic acid at defluorinating conditions of temperature and pressure, and recovering the treated normally liquid paraflinic hydrocarbon mixture.

12. A process for treating propane containing as an impurity a relatively small percentage of organically combined fluorine to remove fluorine therefrom which comprises contacting said propane with chlorosulfonic acid at a temperature of from about -50 to about 150 C.. and recovering the treated propane.

13. A process for treating butane containing as an impurity a relatively small percentage 01' organically combined fluorine to remove fluorine therefrom which comprises contacting said bu-' 8 tane with chlorosulfonic acid at a temperature of from about to about C., and recovering the treated butane.

14. A process for treating a normally liquid paraflinic hydrocarbon mixture containing as an impurity a relatively small percentage of organically combined fluorine to remove fluorine therefrom which comprises contacting said normally liquid paraflinic hydrocarbon mixture with chlorosuli'onic acid at a temperature of from about 50 to about'150" C., and recovering the treated normally liquid paraflinic hydrocarbon mixture.

CARL B. LINN.

REFERENCES CITED The following references are ofrecord in the file of this patent:

UNITED STATES PATENTS OTHER REFERENCES J. A. C. S., 58.: 882-4, June 1936, 3 pages. (Copy in 260--Fluorides.) 

